The present invention relates to a paper feeding apparatus for a printer.
Currently, there have been used paper feeding apparatuses for printers which have various configurations. For example, as shown in FIG. 21, there has been known a paper feeding apparatus in which a pickup roller 202 is rotatably provided on the rocking tip side of a pickup lever 201. The pickup lever 201 has a base end side supported rotatably on a housing. The pickup roller 202 is rotated to feed paper where a rolling contact surface (rubber lining surface) of the pickup roller 202 is pressed against a top paper or sheet S of a paper bundle accommodated and held on a paper guide wall 203 by the rotation of the pickup lever 201.
In a paper feeding apparatus of this type, the pickup roller 202 is urged in the direction of the paper bundle by a spring, which is not shown, and the pressing force of the pickup roller 202 against the paper bundle is set by the spring force of the spring.
In the paper feeding apparatus of this type, moreover, when the paper S is gone and the rolling contact surface of the pickup roller 202 comes in contact with the paper guide wall 203 as shown in FIG. 22, a large frictional force is generated between the pickup roller 202 rotating in a paper feeding direction (a direction of an arrow A) and the paper guide wall 203. By the frictional force, a force for moving in an opposite direction (a direction of an arrow F) to the paper feeding direction is generated on the pickup roller 202, and there is a possibility that the pickup roller 202 might be locked.
In order to avoid locking the pickup roller 202, there has been proposed a paper feeding apparatus which prevents an unnecessary frictional force from being generated. In the paper feeding apparatus, as shown in FIG. 23, a free rotating roller 205 urged by a spring 204 is provided in the paper guide wall 203 opposed to the pickup roller 202. When the paper S is gone, the rolling contact surface of the pickup roller 202 is pushed against the peripheral surface of the free rotating roller 205 so that the pickup roller 202 is rotated together with the free rotating roller 205. As a result, the pickup roller 202 can be thus prevented from being locked (for example, see JP-A-8-259013).
When a pressing force against the paper bundle of a pickup roller is set by a spring force, however, there is a problem in that the pressing force of the pickup roller becomes large when unused paper is pulled out, and it becomes difficult to remove the paper. More specifically, in some cases when the pressing force of the pickup roller against the paper bundle is too great, the pressing force of the pickup roller is greater than a force for feeding the paper by the rotation of the pickup roller so that the pickup roller is locked and the paper cannot be fed out.
Moreover, the amount of flexure of the spring is changed in accordance with the thickness of the paper bundle. For this reason, there is also a problem in that a force for pressing the paper bundle by the roller is changed. For example, when the number of the papers is large, the amount of contraction of the spring is large. Therefore, the spring force is increased so that the pressing force of the roller is increased. On the other hand, when the number of the papers is small, the amount of the contraction of the spring is small, and the spring force is reduced so that the pressing force of the roller is decreased.
As in the paper feeding apparatus described in JP-A-8-259013, moreover, when the free rotating roller 205 urged by the spring 204 is opposed to the pickup roller 202 in the paper guide wall 203, when a second paper S(2) from the last is fed as shown in FIG. 24, the last paper S(1) is held on the paper guide wall 203 side with difficulty since the last paper S(1) comes in contact with the free rotating roller 205 and is thus urged toward the pickup roller 202. As a result, there is a possibility that a so-called “double feed” might occur, that is, two sheets might be fed together.
Also, with the free rotating roller 205 and the spring 204, the number of components is increased.